The present invention relates to a process for improving the performance of liquid membrane separations. More particularly, the present invention pertains to a process for improving the performance of the liquid membrane separations by coating the liquid membrane onto a solid ion-exchange resin in a fixed bed.
It is well known to the art that the ion-exchange separation method can be used to remove ions from a solution. Ion exchange is a chemical reaction in which mobile hydrated ions of a solid are exchanged, equivalent for equivalent, for ions of like charge in solution. The solid has an open, fishnet-like structure, and the mobile ions neutralize the charged, or potentially charged, groups attached to the solid matrix. The solid matrix is termed the ion exchanger.
An ion-exchange membrane, according to the broadest definition, is any ion-exchange material, irrespective of its geometrical form, which can be used as a separation wall between two solutions. Ion-exchange membranes combine the ability to act as a separation wall between two solutions with the chemical and electrochemical properties of ion exchangers. When in contact with electrolyte solutions, the membrane contains a large number of ions. Ions with the same charge as those contained in the exchange membrane are admitted to it, and thus have little difficulty in passing through from one solution to the other. Ions with opposite charge are excluded from the membrane and find it difficult to pass through. The exchange resin is permeated with electrolyte before coating. Thus, the membrane is permselective.
U.S. Pat. No. 3,410,794 to Li discloses a process for separating mixtures into their component parts by means of selective permeation through liquid membranes containing emulsion-forming surfactants. These are usually globules having diameters in a range of 0.2 to 2 mm. These liquid membranes can be one of two types: either water-in-oil-in-water or oil-in-water-in-oil. In general the liquid membranes are used to sequester chemical or biochemical reagents, while allowing reactants to enter the globule where they are trapped or transformed. Further processing is required for reuse of the oil and the stripping solution.
Solid supported liquid membranes are another form of liquid membrane technology for extracting materials from aqueous solutions. An ordinary polymeric membrane is formed from a porous sheet of plastic into which the liquid membrane material is absorbed. This membrane is used to separate the strip solution from the feed solution. The desired ions are carried across the liquid membrane in the plastic pores to the strip solution. The role of the membrane is to select the desired molecule in the feed solution and replace it, equivalent for equivalent, by another ion from the strip solution. This liquid membrane technology can be applied in extraction procedures for a copper and a variety of materials. For instance, a pollutant such as phenol can be trapped within a liquid membrane equipped with appropriate agents. Other materials including uranium and chromate ions have been extracted from solutions using these membranes. Other types of designs are made of solid-state polymers that form a microporous support containing a liquid phase confined by capillary action. These membranes contain specific carriers, liquid ion exchangers that selectively extract the desired material.
Frankenfeld and co-workers have operated a pilot scale waste water treatment process for selective extraction of copper using a water-in-oil-in-water double emulsion. Aqueous extractant droplets are dispersed in an oil containing a surfactant and an ion carrier selective for copper. The resulting emulsion is stirred in a batch of waste water. Recovery and collapse of the extractant emulsion gives a concentrated aqueous copper solution.
Martin and Davies have proposed a similar process for the concentration of copper ore leachates prior to electrowinning. A process has also been proposed in which the liquid membrane is supported on a polymeric membrane. This sacrifices the large interfacial area of the double emulsion for a more stable and more easily formed arrangement.
Legman and Sinfriades have proposed a recovery of copper from aqueous solutions by means of supported liquid membranes. Thus, there remains a need in the art for a method of performing liquid membrane separations which result in the production of a product such as copper ion in high yield.